As is known, a geared hydraulic machine, whether of the type designed to work as a pump or as a motor, generally comprises a body in which a chamber is afforded having a transversal section conformed as a figure of 8 and consisting of two cylindrical chambers which reciprocally intersect, each of which snugly contains a gear that enmeshes with a gear contained in the other chamber.
The body can be cup-shaped, and thus can comprise a single open end, which is closed by a cover comprising the seatings for the support bearings of the gear shafts; the other support bearing of the shafts of the gears being housed in opposite seatings afforded on the bottom of the cup-shaped body. Alternatively, the body can be substantially tubular with two open opposite ends which are closed by a respective cover, each of which comprises the seatings for the bearings of the gear shafts.
In both cases, each cover is generally fixed to the body by means of a plurality of screws or bolts which insert in respective opposite holes afforded in the cover and the body.
The gears sub-divide the internal volume of the hydraulic machine into two operating environments, of which a first environment communicates with an inlet hole of a hydraulic fluid and a second environment communicates with an outlet hole of the hydraulic fluid.
When the hydraulic machine is used as a pump, the fluid is aspirated at low pressure through the inlet hole, is compressed by the rotation of the gears and thus is sent at high pressure through the outlet hole.
When the hydraulic machine is used as a motor, the fluid is supplied at high pressure through the inlet hole, is used to rotate the gears, and is then discharged at low pressure through the outlet hole.
It follows that between the first operating environment of the hydraulic machine, communicating with the inlet hole, and the second operating environment, communication with the outlet hole, a certain pressure difference is always generated which in certain circumstances can reach very high levels.
This pressure difference can cause the deformation of the body of the hydraulic machine and/or the flexion of the gear shafts, from which an increase obtains in the radial distance between the gears, which causes a reduction of the positive displacement efficiency of the hydraulic machine.
The deformation of the body can further cause a displacement of the support bearings in the respective seatings, as well as a reciprocal dealignment of the bearings, especially if the body is cup-shaped, as in this case the deformation of the body is more accentuated at the open end, where the cover is located.
The dealignment is a negative phenomenon inasmuch as it reduces the efficiency of the hydraulic machine and damages the bearings, reducing the working life thereof.
To encounter these drawbacks, a solution has been proposed in which the coupling between each open end of the body and the relative cover is obtained by a non-circular edge, afforded at the open end of the body, which is housed jointedly internally of a corresponding non-circular recess afforded in a continuous flange which projects from the peripheral region of the cover. In this way, the continuous flange of the cover surrounds the edge of the body, opposing the deformation, from the inside towards the outside, to which the open end of the body is subjected due to the internal pressure.
In a further known solution the coupling between each open end of the body and the relative cover is obtained by blocking pins, each of which is housed in respective opposite elongate seatings afforded on the body and the cover. In this way, the blocking pins guarantee reciprocal positioning between the body and the cover, and oppose deformation.
Both these solutions are however rather complicated and expensive. In particular, the mechanical operations required to realise the edge and the corresponding non-circular seating of the first solution are rather complex, and thus require adequate machines and a careful programming thereof.
The mounting of the cover on the body of the second solution, which comprises inserting the blocking pins in the respective seatings, is rather slow and laborious.